History of Pulse code modulation

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	Revision 14 . . December 7, 2001 10:56 pm by The Anome [copyedit, added ADPCM]
	Revision 13 . . December 7, 2001 10:51 pm by The Anome [added extra see-alsos]
	Revision 12 . . (edit) December 7, 2001 10:50 pm by The Anome [copyedit]
	Revision 11 . . December 7, 2001 8:22 pm by (logged).121.100.xxx [linked to compact disc, sampling, polynomial, pseudo random, fixed spelling of occasional, copyedit]
	Revision 10 . . (edit) December 7, 2001 8:16 pm by (logged).121.100.xxx [Linked to nice 'binary' article.]
	Revision 9 . . (edit) December 6, 2001 8:27 am by The Anome [framing bits mentioned]
	Revision 8 . . December 6, 2001 8:25 am by The Anome [Ones-density, precoding, scramblers, DC offset]
	Revision 7 . . (edit) December 6, 2001 8:15 am by The Anome [DPCM is someties Delta PCM - noted]
	Revision 6 . . December 6, 2001 6:26 am by Ap
	Revision 5 . . December 5, 2001 4:06 am by The Anome [mentioned binary code]
	Revision 4 . . December 5, 2001 3:31 am by Ap [further expanded]
	Revision 3 . . December 4, 2001 8:35 am by The Anome [added pointer to modulation index page]
	Revision 2 . . (edit) December 4, 2001 8:33 am by The Anome [Added inline whinge]
	Revision 1 . . December 4, 2001 4:19 am by Ap

Difference (from prior major revision) (author diff)

Changed: 1c1,3

Pulse Code Modulation (PCM) is a digital representation of an analog signal. The signal is sampled? at a sampling frequency f_s. This means the value of the signal, a sample, is captured at uniform distances T (= 1/f_s). Every sample is quantized to a series of symbols in a code in which there are a discrete number of possible symbol values. Where the number of possible values is two, the code is said to be a binary code.

Pulse Code Modulation (PCM) is a digital representation of an analog signal.

The signal is sampled? at a sampling frequency f_s. This means the value of the signal, a sample, is captured at uniform distances T (= 1/f_s). Every sample is quantized to a series of symbols in a code in which there are a discrete number of possible symbol values. Where the number of possible values is two, the code is said to be a binary code.

Changed: 5c7

Differential (or Delta) Pulse Code Modulation (DPCM) encodes the PCM values as differences between the current and the previous value. For audio this type of encoding reduces the number of bits required per sample compared to PCM by about 25%. A variant of DPCM, Adaptive DPCM (ADPCM) varies the size of the quantization step, to allow futher reduction of the required bandwidth for a given signal-to-noise ratio.